Trace Evidence

Summary  Microscopic Analysis  Types of Trace Evidence  Glass  Hair (fur)  Fibers  Paint  Soil  Gunshot Residue

Fibers Fibers are very useful as trace evidence:  Vary widely in class characteristics color, shape, chemical composition, etc.  Easily transferred from one source to another (carpets, clothes, etc.)  Significant persistence (won’t degrade)

How are fibers used as evidence?  As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another. Trace > Fibers

How long do fibers persist? Most fiber evidence is lost (fall off) a short time after the transfer occurs. The fibers that do remain will be persistent. Trace > Fibers

Fibers can be classified into three main categories:  Natural (animal, plant, mineral)  Manufactured  Synthetic Trace > Fibers

Natural Fibers:  Found in nature  Can be artificially colored or treated CottonWoolHemp Trace > Fibers > Natural

Animal Fibers Wool - Hairs from sheep  Most common of animal fibers  Hairs are spun to form thread Silk - comes from silkworm  Spun as double filament (separated before use)  Because of length, doesn’t shed easily Other Hairs from Animals Trace > Fibers > Natural

Plant Fibers Cotton - seed hairs of cotton plant by far most common fiber (find almost everywhere) Under microscope, fibers resemble twisted ribbon Trace > Fibers > Natural

Linen - stem fiber from flax plant Kapok - from seed hairs of kapok plant Other fibers - Manila, hemp, sisal, jute Other Plant Fibers: Trace > Fibers > Natural

Mineral Fibers Asbestos - crystalline material  Used to be used for insulation  Fractures into thin rods that can get into your lungs; can kill you  Not used much anymore Trace > Fibers > Natural

Filament: Long continuous fiber (like silk) Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton) Trace > Fibers Filament vs. Staple

Manufactured Fibers Regenerated Fibers Trace > Fibers > Manufactured Example: Rayon  Cellulose is dissolved, then resolidified to form the polymer fiber  Can occur in filament or staple form

Examples: Nylon and Polyester  Man made  Can also be filament or staple Trace > Fibers > Synthetic Synthetic Fibers

Acrylics  More common as evidence  Usually in staple form  Staples spun together, similar to wool Trace > Fibers > Synthetic Synthetic Fibers

Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Unknown Known Trace > Fibers > Analysis

Fibers from rug in a van. Fibers found on victim. Trace > Fibers > Analysis

Class characteristics Trace > Fibers > Analysis Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed

Refractive Index – n. The ratio of the speed of light in air or in a vacuum to the speed of light in another medium. Other microscopic properties (PLM) Trace > Fibers > Analysis Class characteristics

Chemical Composition: determined by advanced instrumentation Trace > Fibers > Analysis Class characteristics

Glass  What is glass?  What crimes are glass involved in?  How is glass collected?  How is glass analyzed in the lab?

What is glass?  Made from fused inorganic materials  Amorphus; not crystalline (molecules not arranged)  Varies in elemental formula  Many shapes and colors Trace > Glass

How is glass involved in crime?  Small fragments can be used as trace evidence (link objects/people)  Crime scene reconstruction Trace > Glass

How is glass collected?  For reconstruction, detailed photographs can be taken or the entire pane of glass is collected. Trace > Glass

 For trace evidence, usually visually collected with forceps and packaged in plastic bags. Trace > Glass How is glass collected?

 When looking at a radial section, conchoidal fractures point back to the origin of the break  Core usually on opposite side of the origin Trace > Glass For reconstruction: 1. Determine the direction of projectile.

1 2 3 Trace > Glass For reconstruction: 2. Determine the order of projectiles when dealing with more than one.

For trace analysis: Done with microscopic analysis  Color, curve, thickness, etc.  Refractive index: Determined by placing glass in oils of different refractive indexes Trace > Glass Associate unknown glass found at the crime scene with known samples to determine the source.

Refractive index:  Low relief = no outside line R.I. of glass and oil are similar  High relief = thick outside line (Becke line) R.I. of glass and oil are different Trace > Glass

Paint  What is paint?  What crimes are paint involved in?  How is paint collected?  How is paint analyzed in the lab?

What is paint?  Colored chemical coating  Covers cars and houses Trace > Paint

Paint contains 3 things:  Vehicle – binds components together  Pigment – gives paint color  Extenders – used to modify gloss, texture, opacity, etc. What is paint? Trace > Paint

What crimes are paint involved in?  Hit and Runs – paint from car left at scene  Other vehicular accidents  Home invasion – windows; on suspect Trace > Paint

How is paint collected?  Visually by hand or with forceps.  Packaged in sealed containers. Trace > Paint

How is paint analyzed? 1. Possibly a physical match (jigsaw-like) 2. Associate the unknown paint with a known sample (class characteristics) Trace > Paint

Chemical composition determined by FT-IR Trace > Paint > Analysis How is paint analyzed? Chemical “Fingerprint”

Paint can be in multiple layers Each layer is analyzed to determine its physical and chemical properties. Trace > Paint > Analysis

Soil  What is soil?  What crimes involve soil?  How is soil collected?  How is soil analyzed in the lab?

What is soil?  Mixture of animal and vegetable materials, and minerals  In many ways, soil has a unique composition in a given area. Trace > Soil

What crimes involve soil? Due to the widespread location of soil (earth), it can be used to associate people, objects, and scenes in numerous cases. Trace > Soil

How is soil collected & analyzed? Materials in soil are identified and quantified. Analysis relies on soil composition being:  Consistent over time in one location  Different in different locations Trace > Soil Collected in jars or vials.

Gun Shot Residue (GSR)  What is gun shot residue (GSR)?  What crimes are GSR involved in?  How is GSR collected?  How is GSR analyzed in the lab?